FIG. 1 is a principle explanatory drawing showing one example of conventional displacement sensors.
Referring to FIG. 1, reference numeral 101 denotes a magnetic material (a high-electric resistance magnetic material) forming a magnetic path, 102 denotes a space formed within the magnetic material so as to cross the magnetic path, 103 denotes a permanent magnet movably provided in the space, and 104 denotes a Hall device, provided in the magnetic path, for detecting a change of the magnetic flux Φ.
This structure brings on a change of the distribution of the magnetic flux in the magnetic path accompanied with a movement of the permanent magnet 103 in the direction shown by an arrow, and detects the change by the Hall device 104 in order to detect a position of the permanent magnet 103, i.e., a position of the moving body.
FIG. 2 is a principle explanatory drawing showing another example of conventional displacement sensors.
Referring to FIG. 2, reference numeral 111 denotes an E-section magnetic material forming a magnetic path, 112 denotes a coil provided around the base of the central magnetic material fragment of the E-section magnetic material 111, and 113 denotes a non-magnetic single turn coil movably provided around the top of the central magnetic material fragment.
When a high frequency current is fed to the coil 112, this structure generates an oscillating magnetic field, and an induced current in the single turn coil 113 on the basis of the magnetic fluxΦpassing through the magnetic path. But it generates no magnetic flux at the top of the central magnetic material fragment above the single turn coil 113. Intercepting the magnetic field of the magnetic circuit by the induced current flowing in the single turn coil 113 means that an inductance of the magnetic circuit becomes much small. The observation of such a change of the inductance enables detection of the position of the single turn coil that is a movable part.
FIG. 3 is a principle explanatory drawing showing another example of conventional displacement sensors.
Referring to FIG. 3, reference numeral 121 denotes a cylindrical coil wound cylindrically, 122a, 122b denote pickup coils provided within both ends of the cylindrical coil 121, 123 denotes a moving element that is made of a low-electric resistance material, and moves on a shaft of the cylindrical coil 121.
While feeding a high frequency current through the cylindrical coil 121 to generate a magnetic field, on moving the moving element 123, this structure detects by the pickup coils 122a and 122b the distribution of alternating magnetic field changed depending on where the moving element 123 presently is.
The conventional displacement sensors thus arranged as shown in FIG. 1 is reluctant to a high-speed drive to move the permanent magnet, and makes it impossible to build robustly. The displacement sensor shown in FIG. 2 lacks robustness on account of an operation of the single turn coil. Since the displacement sensor shown in FIG. 3 has an air-core cylindrical coil, it cannot expect a heavy output unless a heavy current is fed to the coil. Moreover, it is difficult to design the magnetic field for attaining the linear relationship between displacement and an output signal.